DS5 was doing this the other night with an adult book he'd asked me to read aloud - assuring me he'd like it though I had said he wouldn't. I thought he was asleep, but he was actually quite absorbed (many eyerolls from DS7, who saw nothing appealing in Anita Brookner). He told me how he imagined scenes looked, and places he had been that he was reminded of. I think his fabulous kindy really started his enthusiasm for non-picture books - his teacher read out stories at rest time that were often quite grown up.